1. Field of the Invention
The present invention relates to medical instruments and specifically to a mechanical caliper which is intended for use in conjunction with a heart scale in order to analyze recorded electrocardiograms as disclosed in my U.S. Pat. No. 4,550,502, issued Nov. 5, 1985.
2. Description of the Prior Art
An electrocardiograph is an instrument to be applied to the human body for the purpose of making a graph, or recorded line, for indicating the operations of the heart, such as the expansion and contraction of the heart muscle, which is accompanied by electric currents. The electrocardiograph records the changes of electrical potential occurring in the form of a tracing on a paper chart or strip divided into 1.0 mm square blocks which are representative of units of time (25 mm=1.0 sec. or 1.0 mm=0.040 sec.).
The normal heart rate of an adult is considered to lie between 60 and 100 beats per minute. Slower rates often enable the emergence of extra, irregular beats in a transition to a very rapid heart rate. Fast heart rates, often described as palpitations of the heart, may follow irregular beating and produce weakness, fatigue, anxiety and faintness. The ultimate danger from all types of alterations in the rhythm of the heartbeat of cardiac arrhythmias is the progression of cardiac arrest and sudden death.
A great variety and number of cardiac rhythmic disturbances and disease rhythm mechanisms point up the magnitude of the diagnostic problem facing a physician who must make a definitive diagnosis before selecting a medication to treat the arrhythmia. Also, with the variety of anti-arrhythmic medications available, each possessing its own mode of action and nuance of effect, precise diagnosis of the arrhythmia is most important for selection of optimum therapy.
In view of the magnitude of the problems of accurate diagnosis and matching of medication to the arrhythmia, the need for a diagnostic tool for the study of arrhythmias as recorded on the conventional cardiographic chart or strip is apparent.
Various time intervals on the electrocardiograph (ECG) waveform are of importance, such as heart rate, cycle duration, time of onset of the P-wave to onset of the QRS-wave (PR interval), and the time from the onset of the QRS-wave to the end of the T-wave (QT interval). In order to evaluate these intervals for abnormalities, several measurements and corrections are required which are made by calculations or through the use of reference tables.
Diagnosis of the rhythm requires analysis of the regularity or irregularity of the rhythm, the nature of the irregularities, variation of intervals between beats and comparison of successive intervals, variation of intervals among a series of sequence of beats, separate, respective beating of upper chambers (atria) and lower chambers (ventricles), and the relation between the beating of the atria and the beating of the ventricles.
An instrument is obviously required which enables rapid, accurate measurement of successive intervals between beats and also provides a means for comparison of such intervals.
It is desirable that any such instrument provides the capabilities for simultaneous assessment of a group or series of beats and intervals.
My U.S. Pat. No. 4,550,502 discloses and claims a gauge which facilitates the analysis of a group or sequence of heartbeats recorded on a cardiographic chart in order to diagnose the cardiac rhythm. The guage comprises a flat sheet of transparent material having a plurality, or fan, of straight diverging lines disposed on the sheet; and a plurality of straight parallel lines disposed on the sheet extending in a direction transverse to said diverging lines and perpendicular to a line extending medially between the outermost of said diverging lines. The diverging lines are angularly spaced with respect to one another so as to intercept equal increments along each particular horizontal line. The transverse lines are spacially arranged such that they interact with the diverging lines to form a grid. The distance between adjacent points of intersection with the diverging lines and any of the parallel lines bears a relation to the heartbeat rate or heart cycle interval of a periodic waveform recorded on a cardiographic chart. Indicia are disposed on the sheet for designating the transverse parallel lines as graduations of a scale comprising intervals which correspond to heartbeat cycle intervals or heartbeat rate. The gauge is physically sized so that outermost of the diverging lines are laterally spaced apart to encompass at least six heartbeat cycles of the periodic waveform.
As discussed in that patent, a caliper is described as being utilized to compare successive heart beat cycles. Such a caliper is characterized as an instrument which is adjusted to the interval of a single heartbeat. A limitation on this divider approach however is that such a device is limited in use to examining one beat at a time and then comparing one beat to the next. The dividers of the prior art do not provided for simultaneous analysis of a group or sequence of beats so that the rhythm created by the sequence of beats could be observed and any departure from irregularity would be immediately revealed.
The multi-leg caliper of the present invention solves the problems characterized above and described in my U.S. Pat. No. 4,550,502.
The use of various dividers predates my U.S. Pat. No. 4,550,502. Such use may be found in Italian Patent no. 445,972, dated Mar. 4, 1949, and German Patent no. 269,832, dated Nov. 16, 1950. However, both of these dividers do not allow for direct comparison between multiple points and a chart of any kind directly adjacent thereto.
A number of other divider devices are known, which have members that move about a central pivot point in a fan like shape. Examples of this may be found in French Patent no. 437,458, dated Apr. 22, 1912; U.S. Pat. No. 495,219, dated Apr. 11, 1893; U.S. Pat. No. 3,271,869, dated Sep. 13, 1966; and German Patent no. 240,481, dated Apr. 16, 1946. These all have the distinct disadvantage that all points must move with respect to an upper central pivot point thereby making attachment to a removable scale difficult while precluding compactness in the extended or closed state. Further, many do not allow for movement of the points along a straight line but rather move in an arcuate fashion.
Another type of divider may be found in U.S. Pat. No. 235,225, dated Dec. 7, 1880. While all pivot points in this type of device remain along a straight line during expansion or contraction, unlike the fanlike structure in the previously described patents, this instrument is expressly used for mechanical drafting purposes only. U.S. Pat. No. 774,718, issued Nov. 8, 1904, relates to a ruling machine having pens and pen holders movably supported so as to be adjustable toward and away from each. The pens are used to rule lines on a paper at varying distances apart. Therefore the divider is not actually used for measurement but for producing parallel lines. U.S. Pat. No. 791,235, issued May 30, 1905, is intended for drafting use in the layout of ductwork, plumbing and the like, and as such is exclusively used for dividing a distance into equal parts and not for comparison with scales, charts or the like. British Patent no. 1219, dated Jul. 17, 1913, is similar in concept and use to previously mentioned patent no. 791,235 and is used merely for dividing distances up for use by carpenters, drawing purposes and the like. U.S. Pat. No. 1,643,968, issued Oct. 4, 1927, is used for making optional adjustments in a spaced relation between markers and is again used exclusively for dividing a distance up into a plurality of equidistant spaces. U.S. Pat. No. 1,696,832, issued Dec. 25, 1928, is also used for dividing a distance into a number of equidistant arranged spaces in a single operation. However, none of the above-mentioned patents utilizes the concept of using calipers or dividers for comparison of one distance with respect to another along the same line while simultaneously allowing for direct comparison to a medically related rhythm rule or the like.